Various publications, including patents, published applications, technical articles and scholarly articles are cited throughout the specification. Each of these cited publications is incorporated by reference herein, in its entirety. Full citations for publications not cited fully within the specification are set forth at the end of the specification.
Therapeutic medicine increasingly relies on applications involving artificial or non-self surfaces, like the implantation or extracorporeal use of biomaterials (e.g., hemodialysis filters, medical devices, and drug delivery systems) or the transplantation of cell clusters (e.g., Langerhans islets) (Huebsch, N & D J Mooney, 2009, Nature 462:426-432; Williams, D F, 2009, Biomaterials 30:5897-5909; Korsgren, O & B Nilsson, 2009, Curr Opin Organ Transplant 14:683-687). Although considerable progress has been made in improving the biocompatibility of such non-self materials, their use in medical applications is still hampered by adverse reactions related to the activation of innate immunity and pro-inflammatory pathways; the level of inflammation and associated tissue damage can range from moderate to lethal for the patient (Nilsson, B, O Korsgren, et al., 2010, Trends Immunol 31:32-38; Ratner, B D, 2007, Biomaterials 28:5144-5147). By using soluble complement inhibitors (i.e., compstatin, Sahu, A et al., 1996, J Immunol 157:884-891; Ricklin, D & J D Lambris, 2008, Adv Exp Med Biol 632:273-292) or coating surfaces with heparin, several groups showed that inhibition of complement activation largely attenuates biomaterial-induced activation and surface adhesion of cells (Lappegard, K T et al., 2005, Ann Thorac Surg 79:917-923; Schmidt, S, G et al., 2003, J Biomed Mater Res A 66:491-49910; Nilsson, B, R et al., 1998, Blood 92:1661-1667; Engstad, C S et al., 1997, Thromb Haemost 77:690-696). These observations clearly demonstrate that activation of the complement cascade on biomaterials or cell clusters, and the subsequent cross-talk with cytokine and coagulation pathways, marks a major cause of detrimental inflammatory responses (Nilsson, B, K et al., 2007, Mol Immunol 44:82-94). In particular, the anaphylatoxin C5a is known to potently attract immune cells and trigger their activation, whereas surface-bound C3b is responsible for cell adhesion (Sperling, C et al., 2007, Biomaterials 28:3617-3625; Mollnes, T E et al., 2002, Blood 100:1869-1877). Very recently, the beneficial impact of complement inhibition in clinical biomaterial application was impressively demonstrated for the case of hemodialysis, where addition of compstatin to blood not only inhibited filter-induced complement response but also the subsequent activation of immune cells and the expression of pro-coagulative factors (Kourtzelis, I et al., 2010, Blood 116:631-639). Yet for many applications a continuous administration of soluble inhibitors is not feasible, making modified surfaces with direct autoregulatory activity highly desired.
Recent data indicate that foreign surfaces rapidly adsorb abundant plasma proteins such as human serum albumin (HSA), IgG, and fibrinogen upon contact with blood or tissue, thereby forming an initial monolayer of proteins (Rosengren, A et al., 2002, Biomaterials 23:1237-1247; Collier, T O et al., 1997, Biomed Sci Instrum 33:178-183; Andersson, J et al., 2005, Biomaterials 26:1477-1485) on which complement activation occurs (Andersson, J et al., 2002, J Immunol 168:5786-5791; Liu, L & H Elwing, 1994, J Biomed Mater Res 28:767-773). Whereas the classical pathway is likely to be involved in the initiation of the cascade (Lhotta, K, R et al., 1998, Kidney Int 53:1044-1051; Tengvall, P et al., 1996, Biomaterials 17:1001-1007), e.g., via recognition of adsorbed IgG by C1q, the alternative pathway (AP) appears to be the driving force behind the overall response. For one, adsorption of C3 to the protein layer may induce transformations that enable the formation of initial C3 convertases. Moreover, nascent C3b generated by either pathway binds to HSA and IgG (but not fibrinogen) in the protein layer, thereby leading to the assembly of the main AP convertase, C3bBb, and rapid amplification of complement response (Nilsson, B, K et al., 2007, supra: Andersson, J et at, 2005, supra). The contribution of direct AP activation is further underscored by the observation that hemodialysis treatment of C4-deficient patients can induce complement activation, although at a slower rate compared to complement sufficient individuals (Lhotta, K, R et al., 1998, supra; Lappegard, K T et al., 2004, Ann Thorac Surg 77:932-941). Further, it has been reported that the AP may contribute more than 80% of the C5a and terminal complement complex, C5b-9, that is produced during complement response (Harboe, M, G et al., 2004, Clin Exp Immunol 138:439-446). This observation suggests that the effector phase of complement, following recognition by the CP or the lectin pathway (LP) is indeed dependent on AP-mediated amplification.
Thus, the AP plays a role in the complement-related incompatibility of non-self materials and is considered a suitable target for inhibition aimed at increasing the biocompatibility of these materials. Under homeostatic conditions, complement activation is tightly and precisely controlled by membrane-bound and soluble regulators of complement activation (RCA) (Lambris, J D et al., 2008, Nat Rev Microbial 6:132-142; Ricklin, D et al., 2010, Nat Immunol 11:785-797). Factor H, the second most abundant complement protein in plasma, is the primary regulator of the AP. It is has an elongated structure consisting of 20 homologous short consensus repeats (SCR), each comprising approximately 60 amino acids held together by four conserved cysteine residues. Whereas the complement regulatory functions are concentrated to the N-terminus (SCR 1-4) of factor H, two distinct regions (SCR 7, SCR 19-20) define the recognition of self-surfaces via binding to polyanion patches (e.g., glycosaminoglycans; GAG) on host cells. Factor H regulates the AP by inhibiting the formation of the AP C3 convertase and accelerating its dissociation, or by acting as cofactor for the degradation of C3b by factor I (Wu, J et al., 2009, Nat Immunol 10:728-733; Schmidt, C et al., 2008, J Immunol 181:2610-2619; Schmidt, C et al., 2008, Clin Exp Immunol 151:14-24; Pickering, M C et al., 2008, Clin Exp Immunol 151:210-230; Jozsi, M, & P F Zipfel, 2008, Trends Immunol 29:380-387; Ross, G D et al., 1982, J Immunol 129:2051-2060). In the fluid phase, factor H was reported to have a bent or hairpin-like, rather than a linear structure (Schmidt, C Q et al., 2010, J Mol Biol 395:105-122; Okernefuna, A I et al., 2009, J Mot Biol 391:98-118; Prosser, 13 E et al., 2007, J Exp Med 204:2277-2283; Oppermann, M, T et al., 2006, Clin Exp Immunol 144:342-352).
Surface coating with modulatory proteins or peptides is an approach for increasing biomaterial biocompatibility (Nilsson, P H et al., 2010, Biomaterials 31:4484-4491; Krishna, O D, & K L Kiick, 2010, 94:32-48). Theoretically, biomaterial surface-immobilized RCA proteins should confer a complement-regulatory capacity on the surface and increase its biocompatibility. Indeed, immobilization of the AP regulators factor H and decay accelerating factor (CD55) both attenuated biomaterial-induced complement in previous studies (Andersson, J et al., 2001, Biomaterials 22:2435-2443; Watkins, N J et al., 1997, Immunopharmacology 38:111-118; Andersson, J et al., 2006, J Biomed Mater Res A 76:25-34). However, although feasible to perform on a laboratory scale, the preparation and immobilization of the large RCA proteins is costly and likely associated with great loss of function. As a consequence, this approach would hardly be practical on a commercial scale. An alternative way to increase the blood compatibility of a surface is to conjugate molecules (e.g., antibodies or peptides) with affinity for a plasma protein like factor H or C4b-binding protein (C4BP). The aim for such a procedure is that the structure on the surface should capture its ligand, ideally in an active conformation, when exposed to blood, recruiting a soluble RCA to the artificial surface. Notably, several human pathogens employ recruitment of host regulators as part of their immune evasion strategy (Lambris, J D et al., 2008, supra). A first attempt to utilize this approach for creating a complement-autoregulatory surface was made by Engberg et al., who reported that surface coating with C4BP-binding peptides from Streptococcus pyogenes inhibited complement activation via the CP on a model biomaterial surface (Engberg, A E et al., 2009, Biomaterials 30:2653-2659). Clearly, there is a need for development of additional systems of this type. The present invention satisfies that need.